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Monday, January 27, 2014

The ultraportable laptop that inspired Intel to dream up the marketing label of Ultrabook also lead to a new fashion for small mSATA solid-state drives. With such a slim body it's unsurprising that Apple had to use a new storage form-factor beyond the traditional 2.5in SATA disk for the sake of the MacBook Air.

It didn't use mSATA though. The storage drive Apple chose was actually based on the 1.8in IBM Microdrive, exactly like that which rEVOlutionised personal audio after finding its way into the very first iPod. Alongside the small 1.8in disk, an all-flash model of the Air was available as the flagship model from the start, if only with 60GB capacity. But the die for small form-factor SSDs had been cast, and without the spinning platters of a hard-disk drive, these drives' dimensions could shrink considerably.

Now six years after the first MacBook Air many laptops rely on little mSATA drives, a tiny flash drive using scaled-down Serial ATA-style edge connectors. And following the successful launch of the first triple-level cell (TLC) SSDs last year with the 840 EVO Series, Samsung has now similarly trimmed down its 2.5in drives to mSATA proportions. (For more, see Samsung 840 EVO 750GB review: a triumph in solid-state technology.)

The Samsung 840 EVO mSATA drive is available in four capacities: 120, 250, and 500 GB – plus a new 1 TB configuration that is a world-first for this size of SSD.

Pricing is said to be based on the regular SATA versions from the 840 EVO Series. We found this 500 GB model available for £402 on Amazon, considerably higher than the £244 asked for the standard SATA EVO 500 GB, but at time of testing this SSD is in short supply which will inevitably put up prices initially.

Like its full-size 840 EVO, the mSATA takes 19nm toggle NAND flash, which Samsung deceptively calls '10nm class' to fluff up the spec sheet. And in charge of the flash is again a Samsung-made MEX controller, using a three-core ARM processor. Among its tricks are a scheme to get around the terrible write performance of tri-layer cell NAND flash. Samsung calls it TurboWrite Buffer, and it's made from a part of the main flash cells that's reserved for writes at higher speed. It does this by treating the slow 3-bit MLC flash cells like high-performance SLC cells, in a way the company is unable to explain clearly.

The mSATA format has potential for working across various computing platforms, and even NAS and storage products that can accept small flash drives to accelerate big disks' performance. Samsung aims its computer products exclusively at Windows PCs though, and for these users it offers extra software to accelerate performance further.

Real-time Accelerated Processing of I/O Data – or RAPID – is the backronym for Nvelo's intelligent 'hot data' management, a company bought by Samsung for this software technolgy. It uses more caching from DRAM than is normal in Windows, along with some compression techniques. See all storage device reviews.

We tested a special press sample running custom firmware. This means we can't be sure the results are typical of final retail models, although Samsung's generous history of benchmark grooming should not be ignored.

The results we recorded in the lab were garnered by some of the usual industry benchmark software, and the numbers should speak for themselves.

In the AS SSD test a nominal point score is awarded from eight separate transfer tests. When we reviewed the 750 GB Samsung 840 EVO in standard 2.5in size it scored 1141 points. This new 500 GB mSATA version scored 1147 points which is within the bounds of experimental error to suggest the same overall performance.

Looking more closely at individual results, the full-size SATA version had slightly higher top sequential reads, at 509 against 486 MB/s; and the roles were reversed in write performance, with 481 and 477 MB/s for mSATA and SATA respectively.

Samsung once claims the golden 100,000 IOPS result for this 840 EVO mSATA. Last time around we got close in AS SSD with 93,107 IOPS for 4k reads at 64-thread level. This time we hit 96,662 IOPS, higher but just shy of the notional 100k barrier.

In one important respect, we even saw a major trade upwards in performance. Where QD=1 4k random writes were before capped a little under 100 MB/s for SATA model, the mSATA model reached 142 MB/s here.

And for tyre kickers who just want to see the biggest sequential read/write numbers, the 500 GB Samsung 840 EVO was measured at 536 MB/s writes and 554 MB/s reads, effectively throttled back by the SATA interface itself here in all probablility.